1. Field of the Invention
This invention relates to an irreversible circuit device typified by an isolator or a circulator that is used in a high frequency band such as a microwave band.
2. Description of the Related Art
FIG. 13 of the accompanying drawings is an exploded perspective view of an ordinary isolator (irreversible circuit device) according to the prior art. The isolator 60 shown in the drawing includes a lower yoke 61 and an upper yoke 62, and sandwiches a magnetic member 63, a spacer member 64, a magnetic assembly 65, capacitor substrates 66, 67 and 68, a terminating resistor 69 and a substrate 70 between the upper and lower yokes 62 and 61.
The magnetic assembly 65 in this prior art example includes a magnetic substrate 72 formed of a ferrite sheet, etc, center conductors 73, 74 and 75 arranged on a top surface side of the magnetic substrate 72 and a common electrode connected to these conductors on the back side of the magnetic substrate 72. A slit splits each center conductor 73, 74, 75 into two parts.
Thin sheet-like capacitor substrates 66, 67 and 68 are arranged on the substrate 70. The magnetic assembly 65 is arranged inside these capacitor substrates 66, 67 and 68. A distal end 73a, 74a, 75a of each center conductor 73, 74, 75 of the magnetic assembly 65 is soldered to the capacitor substrate 66, 67, 68 arranged beneath it. A sheet-like spacer member 64 having protuberances 64a and 64a is arranged above the magnetic assembly 65 and a sheet-like magnetic member 63 is arranged on the spacer member 64.
In the isolator of the prior art example shown in FIG. 13, the magnetic member 63 is disposed to apply a bias magnetic field to the magnetic substrate 72. To form a magnetic path of the bias magnetic field from the magnetic member 63, the side end portions of the lower and upper yokes 61 and 62 are bent vertically to form bent portions. The lower and upper yokes 61 and 62 are so shaped as to constitute a box shape as a whole when they are put together.
However, as the device size of the isolator has been reduced year by year in the unit of millimeters (mm), however, positional influences of the yoke side surface portions invite deterioration of uniformity of the bias magnetic field applied to the magnetic substrate 72 because the side surface portions of the yokes and the magnetic substrate 72 are arranged close to one another or because the yoke side surface portions and the magnetic member 63 are arranged close to one another. In consequence, there is problem that performance drops such as the increase of the insertion loss as the isolator.
To allow a uniform bias magnetic field to act on the magnetic substrate 72 in the isolator 60 shown in FIG. 13, it has been customary to shape the magnetic substrate 72 into a size smaller than that of the magnetic member 63 and to let the uniform bias magnetic field act on the magnetic substrate 72 as a whole. Therefore, the size of the magnetic substrate 72 has been set to about 50% of the full width of the isolator 60 in the prior art. To improve performance as the isolator 60, however, there is a problem that the magnetic substrate 72 is preferably as large as possible.
In view of the problems of the prior art described above, it is an object of the invention to provide an irreversible circuit device that can suppress disturbance of a bias magnetic field acting on a peripheral portion of a magnetic substrate by forming a gap portion at sidewall portions of yokes formed of a ferromagnetic materials, can prevent the drop of an insertion loss as an irreversible circuit device, and can reduce an overall size of the device without inviting the drop of the insertion loss.
In view of the problems of the prior art described above, it is another object of the invention to provide an irreversible circuit device that can suppress disturbance of a bias magnetic field acting on a peripheral portion of a magnetic substrate by forming a gap portion at sidewall portions of yokes formed of a ferromagnetic materials, can prevent the drop of an insertion loss as an irreversible circuit device, can reduce an overall size of the device without inviting the drop of the insertion loss and can improve performance by increasing as much as possible the size of the magnetic substrate.
To accomplish the objects described above, one aspect of the invention provides an irreversible circuit device comprising a yoke main body having sidewall portions defined by an upper yoke and a lower yoke, and accommodating therein a magnetic substrate, a plurality of line conductors arranged on a main plane of the magnetic substrate while being individually insulated from one another, a plurality of capacitor substrates arranged around the magnetic substrate and a magnetic member for applying a DC bias magnetic field in substantially a vertical direction to the main plane of the magnetic substrate, wherein the line conductors are put one upon another on the main surface side of the magnetic substrate and are connected to one another on the other surface side of the magnetic substrate, each end of the line conductors put one upon another on the main surface side of the magnetic substrate is connected to the capacitor substrate, and a gap portion for magnetically insulating the upper yoke and the lower yoke is formed on the sidewall portion of the yoke main body.
When the gap portion for magnetically isolating the upper yoke and the lower yoke is interposed between them, magnetic interference between the magnetic member and the sidewall portions of the upper and lower yokes and between the magnetic substrate and the sidewall portions of the upper and lower yokes does not easily occur, and disturbance of the bias magnetic field acting on from the magnetic member to the magnetic substrate can be reduced even when the irreversible circuit device is rendered compact in size. Eventually, the insertion loss can be suppressed. Because disturbance of the bias magnetic field can be thus suppressed, the sidewall portions of the yoke main body can be brought closer to the magnetic member or to the magnetic substrate than in the prior art construction, and the size of the irreversible circuit device can be reduced.
To accomplish the objects described above, another aspect of the invention provides an irreversible circuit device comprising a yoke main body having sidewall portions defined by an upper yoke and a lower yoke, and accommodating therein a magnetic substrate, a plurality of line conductors arranged on a main plane of the magnetic substrate while being individually insulated from one another, a plurality of capacitor substrates arranged around the magnetic substrate and a magnetic member for applying a DC bias magnetic field in substantially a vertical direction to the main plane of the magnetic substrate, wherein the line conductors are put one upon another on the main surface side of the magnetic substrate and are connected to one another on one of surface sides of the magnetic substrate, each end of the line conductors put one upon another on the main surface side of the magnetic substrate is connected to the capacitor substrate, the magnetic substrate is formed into a rectangular shape as viewed in a plan view, the length of a major side of the rectangular magnetic substrate is set to a length within the range of 65 to 100% of an inner diameter of the yoke main body, and a gap portion for magnetically insulating the upper yoke and the lower yoke is formed on the sidewall portion of the yoke main body.
When the gap portion for magnetically isolating the upper yoke and the lower yoke is interposed between them, magnetic interference between the magnetic member and the sidewall portions of the upper and lower yokes and between the magnetic substrate and the sidewall portions of the upper and lower yokes does not easily occur, and disturbance of the bias magnetic field acting on the magnetic substrate from the magnetic member can be reduced even when the irreversible circuit device is rendered compact in size. Eventually, the insertion loss can be suppressed. Because disturbance of the bias magnetic field can be thus suppressed, the distance from the sidewall portions to the magnetic member or to the magnetic substrate can be much more decreased, and the size of the irreversible circuit device can be reduced. In addition, because disturbance of the bias magnetic field can be reduced, the size of the magnetic substrate can be increased much more than ever, and performance of the irreversible circuit device can be improved.
To solve the problems described above, the gap portion described above is arranged in a region of the sidewall portion of the yoke main body adjacent to a side surface of the magnetic substrate.
Because the gap portion is arranged in the adjacent region of the magnetic substrate, even when the magnetic substrate and the sidewall portions of the yokes can be brought closer to one another and in a compact construction, and disturbance of the magnetic field does not easily occur.
To solve the problems described above, the yoke main body is shaped into a box shape by the upper yoke, the lower yoke and resin molded portions provided accessorily to the upper and lower yokes.
Because the sidewall portions of the yokes do not exist at portions where the gap portion is provided, a resin molded portion not having magnetic influences is preferably arranged to retain the overall shape of the yokes. In consequence, the shape as the yokes can be retained without affecting the bias magnetic field.
To solve the problems described above, a height of the side surface of the yoke main body of portions exclusive of a thickness of the gap portion in the yoke main body is not greater than a thickness of a magnetic member accommodated inside the yoke main body.
The thickness of the gap portion is preferably great. However, good characteristics can be easily obtained when the height of the side surface of the yoke main body exclusive of the thickness of the gap portion is smaller than the thickness of the magnetic member.